EAL

DM: Prevention of Type 2 Diabetes (2007)

Citation:

Study Design:

Class:

- Click here for explanation of classification scheme.

Quality Rating:

Research Purpose:

This study was done to examine prospectively the relationship between glycemic diets, low fiber intake, and risk of non-insulin-dependent diabetes mellitus.

Inclusion Criteria:

1. Subjects responding to the 1986 food frequency questionnaire (FFQ) with 134 food items.

2. Consumed 800 to 3500 kcal on FFQ

Exclusion Criteria:

1. Diabetes melliltus

2. Cancer

3. Myocardial infarction

4. Angina

5. Stroke

6. Coronary artery surgery

7. Left >=10 items blank on the FFQ

Description of Study Protocol:

Recruitment: Nurses' Health Study participants, based on completion of a 1986 expanded food frequency questionnaire.

Design: Cohort Study.

1. Dietary assessment:

a. In 1986 subjects completed a validated FFQ containing 134 food items.

b. Calculation of average glycemic index for each participant by summing the products of the carbohydrate content per serving for each food times the average number of servings of that food per day, times its glycemic index, all divided by the total amount of carbohydrate daily intake.

2. Participants provided self-reported weight smoking status and physical activity information in 1986.

3. Follow-up questionnaires were done in 1988, 1990, 1992 to determine if subjects had been diagnosed with type 2 diabetes melllitus using the following criteria:

a. >1 classical clinical symptoms

b. >2 elevated plasma glucose concentrations on different occasions: Fasting: >140 mg/dl 2-hr: >200 mg/dl Random: >200 mg/dl

c. treatment with hypoglycemic medications.

Blinding Used (if applicable): not applicable

Intervention (if applicable): Initial and follow-up questionnaires.

Statistical Analysis:

Relative Risks (RRs) were calculated by dividing the incidence rate of NIDDM in a particular category of exposure by the corresponding rate in the reference category. Relative risks were simultaneously adjusted for other variables by means of logistic regression analysis. The Mantel extension test was calculated to assess the linear trend with increasing exposure levels.

Data Collection Summary:

Timing of Measurements:

Initial FFQ was completed in 1986 as well as reported weight, smoking status and physical activity. Follow-up questionnaires to determine newly diagnosed diabetes were done every two years after the 1986 FFQ (1988, 1990, 1992).

Dependent Variables:

Diagnosis of Type 2 diabetes mellitus

Independent Variables:

Cereal Fiber intake
Glycemic Load

Control Variables:

Age
BMI
Smoking
Physical Activity
Family History of Diabetes
Alcohol and Cereal Fiber Intake
Total Energy Intake

Description of Actual Data Sample:

Initial N: 65,173 women completed the 1986 expanded FFQ

Attrition (Final N): 65,173 women were followed for 6-yr, 1986-1992

Age: Aged 30 - 55 years at enrollment, subjects in analysis aged 40 - 65 years

Ethnicity: not mentioned

Other Relevant Demographics: Women from the Nurses' Health Study

Anthropometrics:

Location: United States

Summary of Results:

Other Findings

915 (1.4%) cases of type 2 diabetes mellitus were identified among the population of 65,173 women.

The dietary glycemic index was positively associated with risk of diabetes after adjustment for age, BMI, smoking, physical activity, family history of diabetes, alcohol and cereal fiber intake, and total energy intake.

Comparing the highest with the lowest quintile, the RR of diabetes was 1.37 (95% CI, 1.09-1.71, P for trend = 0.005).

The glycemic load was also positively associated with diabetes (RR=1.47, 95% CI, 1.16-1.86, P for trend=0.003).

There was a significant inverse association between total dietary fiber intake and risk of NIDDM (p= .02). Cereal fiber intake was inversely associated with risk of diabetes when comparing the extreme quintiles (RR=0.72, 95% CI, 0.58-0.90, P for trend = 0.001)

The combination of a high glycemic load and a low cereal fiber intake further increased the risk of diabetes (RR=2.50, 95% CI, 1.14-5.51) when compared with a low gylcemic load and high cereal fiber intake.

Animal fat intake was unrelated with risk of NIDDM, whereas vegetable fat was inversely assosicated with risk of NIDDM, although it was not statistically significant.

Author Conclusion:

Our results support the hypothesis that diets with a high glycemic load and a low cereal fiber content increase risk of diabetes in women. Further, the results suggest that grains should be consumed in a minimally refined form to reduce the incidence of diabetes.

Funding Source:

Government:	NIH, Instituto Mexicano del Seguro Social
University/Hospital:	Harvard School of Public Health, Instituto Mexicano del segurao Social (Mexico), Brigham and women's Hospital and Harvard Medical School

Reviewer Comments:

This study found that a dietary intake with a high glycemic load and low in total dietary fiber, especially cereal fiber, increased the risk of non-insuin dependent diabetes mellitus. Saturated fat intake was unrelated with the risk of NIDDM. Measurement error of a food frequency questionnaire must be kept in mind when considering these results.

Quality Criteria Checklist: Primary Research
Relevance Questions
	1.	Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies)	Yes
	2.	Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about?	Yes
	3.	Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice?	Yes
	4.	Is the intervention or procedure feasible? (NA for some epidemiological studies)	Yes

Validity Questions
1.	Was the research question clearly stated?		Yes
	1.1.	Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified?	Yes
	1.2.	Was (were) the outcome(s) [dependent variable(s)] clearly indicated?	Yes
	1.3.	Were the target population and setting specified?	Yes
2.	Was the selection of study subjects/patients free from bias?		Yes
	2.1.	Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study?	Yes
	2.2.	Were criteria applied equally to all study groups?	Yes
	2.3.	Were health, demographics, and other characteristics of subjects described?	Yes
	2.4.	Were the subjects/patients a representative sample of the relevant population?	Yes
3.	Were study groups comparable?		Yes
	3.1.	Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT)	N/A
	3.2.	Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline?	N/A
	3.3.	Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.)	No
	3.4.	If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis?	Yes
	3.5.	If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.)	N/A
	3.6.	If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")?	N/A
4.	Was method of handling withdrawals described?		Yes
	4.1.	Were follow-up methods described and the same for all groups?	Yes
	4.2.	Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.)	Yes
	4.3.	Were all enrolled subjects/patients (in the original sample) accounted for?	Yes
	4.4.	Were reasons for withdrawals similar across groups?	Yes
	4.5.	If diagnostic test, was decision to perform reference test not dependent on results of test under study?	N/A
5.	Was blinding used to prevent introduction of bias?		N/A
	5.1.	In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate?	N/A
	5.2.	Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.)	N/A
	5.3.	In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded?	N/A
	5.4.	In case control study, was case definition explicit and case ascertainment not influenced by exposure status?	N/A
	5.5.	In diagnostic study, were test results blinded to patient history and other test results?	N/A
6.	Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described?		N/A
	6.1.	In RCT or other intervention trial, were protocols described for all regimens studied?	N/A
	6.2.	In observational study, were interventions, study settings, and clinicians/provider described?	N/A
	6.3.	Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect?	N/A
	6.4.	Was the amount of exposure and, if relevant, subject/patient compliance measured?	N/A
	6.5.	Were co-interventions (e.g., ancillary treatments, other therapies) described?	N/A
	6.6.	Were extra or unplanned treatments described?	N/A
	6.7.	Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups?	N/A
	6.8.	In diagnostic study, were details of test administration and replication sufficient?	N/A
7.	Were outcomes clearly defined and the measurements valid and reliable?		Yes
	7.1.	Were primary and secondary endpoints described and relevant to the question?	Yes
	7.2.	Were nutrition measures appropriate to question and outcomes of concern?	???
	7.3.	Was the period of follow-up long enough for important outcome(s) to occur?	Yes
	7.4.	Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures?	Yes
	7.5.	Was the measurement of effect at an appropriate level of precision?	???
	7.6.	Were other factors accounted for (measured) that could affect outcomes?	Yes
	7.7.	Were the measurements conducted consistently across groups?	Yes
8.	Was the statistical analysis appropriate for the study design and type of outcome indicators?		Yes
	8.1.	Were statistical analyses adequately described and the results reported appropriately?	Yes
	8.2.	Were correct statistical tests used and assumptions of test not violated?	Yes
	8.3.	Were statistics reported with levels of significance and/or confidence intervals?	Yes
	8.4.	Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)?	N/A
	8.5.	Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)?	Yes
	8.6.	Was clinical significance as well as statistical significance reported?	Yes
	8.7.	If negative findings, was a power calculation reported to address type 2 error?	N/A
9.	Are conclusions supported by results with biases and limitations taken into consideration?		Yes
	9.1.	Is there a discussion of findings?	Yes
	9.2.	Are biases and study limitations identified and discussed?	Yes
10.	Is bias due to study's funding or sponsorship unlikely?		Yes
	10.1.	Were sources of funding and investigators' affiliations described?	Yes
	10.2.	Was the study free from apparent conflict of interest?	Yes